Contents

Linux Input drivers v1.0

(c) 1999-2001 Vojtech Pavlik vojtech@ucw.cz

Sponsored by SuSE

0. Disclaimer

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option)
any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc., 59
Temple Place, Suite 330, Boston, MA 02111-1307 USA

Should you need to contact me, the author, you can do so either by e-mail

  • mail your message to <vojtech@ucw.cz>, or by paper mail: Vojtech Pavlik,
    Simunkova 1594, Prague 8, 182 00 Czech Republic

For your convenience, the GNU General Public License version 2 is included
in the package: See the file COPYING.

1. Introduction

This is a collection of drivers that is designed to support all input
devices under Linux. While it is currently used only on for USB input
devices, future use (say 2.5/2.6) is expected to expand to replace
most of the existing input system, which is why it lives in
drivers/input/ instead of drivers/usb/.

The centre of the input drivers is the input module, which must be
loaded before any other of the input modules - it serves as a way of
communication between two groups of modules:

1.1 Device drivers

These modules talk to the hardware (for example via USB), and provide
events (keystrokes, mouse movements) to the input module.

1.2 Event handlers

These modules get events from input and pass them where needed via
various interfaces - keystrokes to the kernel, mouse movements via a
simulated PS/2 interface to GPM and X and so on.

2. Simple Usage

For the most usual configuration, with one USB mouse and one USB keyboard,
you’ll have to load the following modules (or have them built in to the
kernel):

  1. input
  2. mousedev
  3. keybdev
  4. usbcore
  5. uhci_hcd or ohci_hcd or ehci_hcd
  6. usbhid

After this, the USB keyboard will work straight away, and the USB mouse
will be available as a character device on major 13, minor 63:

  1. crw-r--r--   1 root     root      13,  63 Mar 28 22:45 mice

This device has to be created.
The commands to create it by hand are:

  1. cd /dev
  2. mkdir input
  3. mknod input/mice c 13 63

After that you have to point GPM (the textmode mouse cut&paste tool) and
XFree to this device to use it - GPM should be called like:

  1. gpm -t ps2 -m /dev/input/mice

And in X:

  1. Section "Pointer"
  2.     Protocol    "ImPS/2"
  3.     Device      "/dev/input/mice"
  4.     ZAxisMapping 4 5
  5. EndSection

When you do all of the above, you can use your USB mouse and keyboard.

3. Detailed Description

3.1 Device drivers

Device drivers are the modules that generate events. The events are
however not useful without being handled, so you also will need to use some
of the modules from section 3.2.

3.1.1 usbhid

usbhid is the largest and most complex driver of the whole suite. It
handles all HID devices, and because there is a very wide variety of them,
and because the USB HID specification isn’t simple, it needs to be this big.

Currently, it handles USB mice, joysticks, gamepads, steering wheels
keyboards, trackballs and digitizers.

However, USB uses HID also for monitor controls, speaker controls, UPSs,
LCDs and many other purposes.

The monitor and speaker controls should be easy to add to the hid/input
interface, but for the UPSs and LCDs it doesn’t make much sense. For this,
the hiddev interface was designed. See Documentation/hid/hiddev.txt
for more information about it.

The usage of the usbhid module is very simple, it takes no parameters,
detects everything automatically and when a HID device is inserted, it
detects it appropriately.

However, because the devices vary wildly, you might happen to have a
device that doesn’t work well. In that case #define DEBUG at the beginning
of hid-core.c and send me the syslog traces.

3.1.2 usbmouse

For embedded systems, for mice with broken HID descriptors and just any
other use when the big usbhid wouldn’t be a good choice, there is the
usbmouse driver. It handles USB mice only. It uses a simpler HIDBP
protocol. This also means the mice must support this simpler protocol. Not
all do. If you don’t have any strong reason to use this module, use usbhid
instead.

3.1.3 usbkbd

Much like usbmouse, this module talks to keyboards with a simplified
HIDBP protocol. It’s smaller, but doesn’t support any extra special keys.
Use usbhid instead if there isn’t any special reason to use this.

3.1.4 wacom

This is a driver for Wacom Graphire and Intuos tablets. Not for Wacom
PenPartner, that one is handled by the HID driver. Although the Intuos and
Graphire tablets claim that they are HID tablets as well, they are not and
thus need this specific driver.

3.1.5 iforce

A driver for I-Force joysticks and wheels, both over USB and RS232.
It includes ForceFeedback support now, even though Immersion
Corp. considers the protocol a trade secret and won’t disclose a word
about it.

3.2 Event handlers

Event handlers distribute the events from the devices to userland and
kernel, as needed.

3.2.1 keybdev

keybdev is currently a rather ugly hack that translates the input
events into architecture-specific keyboard raw mode (Xlated AT Set2 on
x86), and passes them into the handle_scancode function of the
keyboard.c module. This works well enough on all architectures that
keybdev can generate rawmode on, other architectures can be added to
it.

The right way would be to pass the events to keyboard.c directly,
best if keyboard.c would itself be an event handler. This is done in
the input patch, available on the webpage mentioned below.

3.2.2 mousedev

mousedev is also a hack to make programs that use mouse input
work. It takes events from either mice or digitizers/tablets and makes
a PS/2-style (a la /dev/psaux) mouse device available to the
userland. Ideally, the programs could use a more reasonable interface,
for example evdev

Mousedev devices in /dev/input (as shown above) are:

  1. crw-r--r--   1 root     root      13,  32 Mar 28 22:45 mouse0
  2. crw-r--r--   1 root     root      13,  33 Mar 29 00:41 mouse1
  3. crw-r--r--   1 root     root      13,  34 Mar 29 00:41 mouse2
  4. crw-r--r--   1 root     root      13,  35 Apr  1 10:50 mouse3
  5. ...
  6. ...
  7. crw-r--r--   1 root     root      13,  62 Apr  1 10:50 mouse30
  8. crw-r--r--   1 root     root      13,  63 Apr  1 10:50 mice

Each ‘mouse’ device is assigned to a single mouse or digitizer, except
the last one - ‘mice’. This single character device is shared by all
mice and digitizers, and even if none are connected, the device is
present. This is useful for hotplugging USB mice, so that programs
can open the device even when no mice are present.

CONFIG_INPUT_MOUSEDEV_SCREEN_[XY] in the kernel configuration are
the size of your screen (in pixels) in XFree86. This is needed if you
want to use your digitizer in X, because its movement is sent to X
via a virtual PS/2 mouse and thus needs to be scaled
accordingly. These values won’t be used if you use a mouse only.

Mousedev will generate either PS/2, ImPS/2 (Microsoft IntelliMouse) or
ExplorerPS/2 (IntelliMouse Explorer) protocols, depending on what the
program reading the data wishes. You can set GPM and X to any of
these. You’ll need ImPS/2 if you want to make use of a wheel on a USB
mouse and ExplorerPS/2 if you want to use extra (up to 5) buttons.

3.2.3 joydev

Joydev implements v0.x and v1.x Linux joystick api, much like
drivers/char/joystick/joystick.c used to in earlier versions. See
joystick-api.txt in the Documentation subdirectory for details. As
soon as any joystick is connected, it can be accessed in /dev/input
on:

  1. crw-r--r--   1 root     root      13,   0 Apr  1 10:50 js0
  2. crw-r--r--   1 root     root      13,   1 Apr  1 10:50 js1
  3. crw-r--r--   1 root     root      13,   2 Apr  1 10:50 js2
  4. crw-r--r--   1 root     root      13,   3 Apr  1 10:50 js3
  5. ...

And so on up to js31.

3.2.4 evdev

evdev is the generic input event interface. It passes the events
generated in the kernel straight to the program, with timestamps. The
API is still evolving, but should be usable now. It’s described in
section 5.

This should be the way for GPM and X to get keyboard and mouse
events. It allows for multihead in X without any specific multihead
kernel support. The event codes are the same on all architectures and
are hardware independent.

The devices are in /dev/input:

  1. crw-r--r--   1 root     root      13,  64 Apr  1 10:49 event0
  2. crw-r--r--   1 root     root      13,  65 Apr  1 10:50 event1
  3. crw-r--r--   1 root     root      13,  66 Apr  1 10:50 event2
  4. crw-r--r--   1 root     root      13,  67 Apr  1 10:50 event3
  5. ...

And so on up to event31.

4. Verifying if it works

Typing a couple keys on the keyboard should be enough to check that
a USB keyboard works and is correctly connected to the kernel keyboard
driver.

Doing a “cat /dev/input/mouse0” (c, 13, 32) will verify that a mouse
is also emulated; characters should appear if you move it.

You can test the joystick emulation with the ‘jstest’ utility,
available in the joystick package (see Documentation/input/joystick.txt).

You can test the event devices with the ‘evtest’ utility available
in the LinuxConsole project CVS archive (see the URL below).

5. Event interface

Should you want to add event device support into any application (X, gpm,
svgalib …) I <vojtech@ucw.cz> will be happy to provide you any help I
can. Here goes a description of the current state of things, which is going
to be extended, but not changed incompatibly as time goes:

You can use blocking and nonblocking reads, also select() on the
/dev/input/eventX devices, and you’ll always get a whole number of input
events on a read. Their layout is:

  1. struct input_event {
  2.     struct timeval time;
  3.     unsigned short type;
  4.     unsigned short code;
  5.     unsigned int value;
  6. };

‘time’ is the timestamp, it returns the time at which the event happened.
Type is for example EV_REL for relative moment, EV_KEY for a keypress or
release. More types are defined in include/linux/input.h.

‘code’ is event code, for example REL_X or KEY_BACKSPACE, again a complete
list is in include/linux/input.h.

‘value’ is the value the event carries. Either a relative change for
EV_REL, absolute new value for EV_ABS (joysticks …), or 0 for EV_KEY for
release, 1 for keypress and 2 for autorepeat.